This invention relates to an active notch filter circuit employing switched-capacitor resistors and more particularly to such filter circuits that include simultaneously-digitally-programmable capacitor arrays for controlling notch width and notch depth.
Notch filters are used in analog-signal manipulating circuits for rejecting a particular signal frequency, or narrow range of frequencies. Conventional notch filters have a center or primary rejection frequency w, and a quality factor Q, which when high corresponds to a narrow filter bandwidth and when low corresponds to a relatively wide bandwidth. A high and low Q value also corresponds respectively to a narrow notch and a wide notch, as is further explained below. The transfer function of the conventional notch filter is expressed as ##EQU1##
Notch filters of this kind are described by Alan B. Grebene in his book Bipolar And MOS Analog Integrated Circuit Design, 1984, pages 736-739.
Notch width and notch depth are typically established by the filter manufacturer and are not controllable by the filter user.
It is an object of this invention to provide a notch filter circuit that is programmable with respect to notch width and depth.
It is a further object of this invention to provide such a filter wherein notch width and notch depth are independently programmable by the user.